The present invention relates to nonwoven, air-laid fabrics formed predominantly of textile length synthetic fibers, the method of making the same, and products formed therefrom. The present invention also relates to disposable absorbent articles such as disposable diapers, incontinent pads, sanitary napkins, nursing pads, and the like, utilizing the fibrous web produced.
Despite the advanced state of the art of liquid-pervious, resin-bonded, nonwoven fabrics, a satisfactory method of producing such a fabric having very low density and high loft, and which is liquid pervious, has not been developed previously.
Disposable absorbent articles such as disposable diapers, provide substantial advantages and convenience over diapers that have to be laundered and reused, particularly when the diapers are used away from home. In recent years, many different disposable diapers have been proposed and some have been successful in the marketplace. However, even the successful diapers may be inadequate in some of the functioning properties, and their commercial success has come, at least in part, because consumers have been willing to accept inadequate performance as part of the price for convenience.
One design criterion which has not heretofore been met adequately is keeping moisture away from the surface of the diaper which comes into contact with the infant's skin. The portion of the diaper nearest the infant's skin is generally identified as the facing layer. Ideally, the facing layer should permit a void of urine to rapidly permeate the layer, but after permeation of the layer, the facing should not permit the wetness to come back through the facing to the infant's skin.
One disposable diaper representing a significant advance in the art, is a multi-layer diaper comprising, in order, a fibrous facing layer which is to be brought into contact with the infant's skin; a layer of highly porous, loosely compacted, cellulosic batt; a paper-like densified, highly compacted batt; and a moisture-impervious backing sheet adhered to the densified layer at the interface therebetween. The facing layer is of porous construction and its fibers have less wettability for water than the fibers of the loosely compacted batt, resulting in a tendency for liquid to flow from the facing layer into the batt. The densified fibrous layer has a smaller average pore size than the loosely compacted batt, resulting in a tendency for liquid to flow preferentially from the batt into the underlying densified layer rather than to other areas of the batt, thus tending to restrict wetting in the batt to an area of moderate size. Liquid flowing into the densified layer tends to spread laterally because of the wicking action of the densified layer and liquid which might pass through the densified layer during discharge is held back by the impervious backing sheet usually for a sufficient time to permit absorption to take place. Liquid in excess of the absorptive capacity of the densified layer is forced back by the impervious layer into the dry portion of the loosely compacted batt, thus utilizing the additional absorptive capacity therein.
However, while the diaper structure described above presents a significant advance in the art, during heavy periods of discharge, after the densified layer and integral loosely compacted batt become wetted to a high level, there is a tendency to wet back into the facing layer. When the facing layer becomes wet, the urine wets the infant's skin and discomfort or irritation can take place. It has been found that a low density, resin-bonded, nonwoven fabric of resilient synthetic fibers permits the liquid to pass through the fabric rapidly, but the fabric is not readily rewetted.
Nonwoven materials are structures which, in general, consist of an assemblage or web of fibers, joined randomly or systematically by mechanical, chemical or other means. These materials are well known in the art, having gained considerable prominence within the last twenty years or so in the consumer market, industrial commercial market, and the hospital field.
There are two basic techniques for forming individual fibers into webs or sheets to provide nonwoven materials such as nonwoven fabrics. One method is the wet laying of fibers on a screen or wire to form paper or paper-like sheets. The other method which is of particular interest herein is laying the fibers in a dry condition either by carding or air-blowing against a foraminous support. Frequently a binder is added to assist in holding the fibers in place. The latter dry-formed webs are generally of a lesser density with a high loft and are more liquid pervious than the paper-like sheets.
Generally, when a fibrous web is dry laid, it is in an unstabilized state, for instance, wherein the fibers are carried in an air stream and deposited on a foraminous belt or cylinder. Thereafter, the web can be bonded by impregnating the same with a binder throughout. The weight of the binder material, as well as the application technique, tend to compact the web somewhat, thus increasing the web density and reducing its bulk.